Unprecedented Scissor Effect of Macromolecular Cross-linkers on the Glass Transition Temperature of Poly(N-vinylimidazole), Crystallinity Suppression of Poly(tetrahydrofuran) and Molecular Mobility by Solid State NMR in Poly(N-vinylimidazole)-l-poly(tetrahydrofuran) Conetworks

Unexpected correlations have been found between structural parameters and glass transition temperatures (Tg) of poly(N-vinylimidazole) (PVIm) and crystallinity of poly(tetrahydrofuran) (PTHF) in a series of novel, unique PVIm-l-PTHF amphiphilic conetworks synthesized in broad composition ranges via free radical copolymerisation of VIm and semicrystalline, methacrylate-telechelic PTHF macromolecular cross-linkers with varying Mn from 2170 to 10 000 g mol−1. Differential scanning calorimetry (DSC) investigations revealed microphase separation between the covalently bonded PVIm and PTHF components, that is two distinct Tgs corresponding to the respective polymers (PVIm and PTHF) were obtained in these optically clear, transparent materials. Complete microphase separation, i.e. absence of mixed phases, was also confirmed by solid state NMR measurements. The Tg of the PVIm phase significantly decreases with increasing PTHF content, and Fox–Flory type correlation was surprisingly found between the Tg of PVIm and its Mc (average molecular weight between cross-links). This striking finding indicates a unique, unpredicted scissor effect of the macromolecular PTHF cross-linker in these materials, i.e. with respect to glass transition, PVIm behaves as individual chains between cross-links. The molecular mobility in the PVIm chain segments obtained by solid state NMR investigations shows a similar trend as a function of Mc. In the DSC thermograms, the semicrystalline PTHF has a sharp endothermic melting peak (Tm) indicating partial crystallisation of this polymer. It was found that the Tm and the crystalline fraction (Xc) of the PTHF phase are suppressed by even a minimal content of PVIm phase in the conetworks. Even complete diminishing of Xc occurs in conetworks with lower than 40 wt% PTHF of the lowest Mn (2170 g mol−1). Unexpectedly, Tm linearly decreases with Mc in conetworks with constant Mn of PTHF. These data indicate that the decrease of both Tm and Xc of PTHF is not only composition dependent, but the MW of the macromolecular PTHF cross-linker and the Mc of the PVIm component also have effects on these parameters. These results also indicate that chemical bonding of polymer chains in conetworks yields novel materials with unprecedented property variation. This provides unique opportunities for fine tuning of the investigated fundamental material properties, i.e. Tg, Tm and Xc, within certain ranges in the novel PVIm-l-PTHF amphiphilic conetworks by selecting the proper synthesis parameters, that is, composition and MW of the telechelic PTHF macromonomer cross-linker

Thermally Responsive Amphiphilic Conetworks and Gels Based on Poly(N‑isopropylacrylamide) and Polyisobutylene

Novel amphiphilic conetworks (APCN) consisting of thermoresponsive poly(N-isoproplyacrylamide) (PNiPAAm) cross-linked by hydrophobic methacrylate-telechelic polyisobutylene (MA-PIB-MA) were successfully synthesized in a broad composition range. The resulting PNiPAAm-l-PIB conetworks (“l” stands for “linked by”) were obtained by radical copolymerization of NiPAAm with MA-PIB-MA in tetrahydrofuran, a cosolvent for all the components. Low amounts of extractables substantiated efficient network formation. The composition dependent two glass transition temperatures (Tg) by DSC analysis indicate microphase separation of the cross-linked components without mixed phases. It was found that the PNiPAAm-l-PIB conetworks are uniformly swellable in both water and n-hexane; i.e., these new materials behave either as hydrogels or as hydrophobic gels in aqueous or nonpolar media, respectively. The uniform swelling in both polar and nonpolar solutes indicates cocontinuous (bicontinuous) phase morphology. The equilibrium swelling degrees (R) depend on composition, that is, the higher the PIB content, the lower the R in water and the higher in n-hexane. The PNiPAAm phase keeps its thermoresponsive behavior in the conetworks as shown by significant decrease of the swelling degree in water between 20 and 35 °C. The lower critical solubility temperature (LCST) values determined by DSC are found to decrease from 34.1 °C (for the pure PNiPAAm homopolymer) to the range of 25–28 °C in the conetworks, and the extent of the LCST decrease is proportional with the PIB content. Deswelling-swelling, i.e., heating–cooling, cycle indicates insignificant hysteresis in these new thermoresponsive materials. This indicates that PNiPAAm-l-PIB conetworks with predetermined and thermoresponsive swelling behavior can be designed and utilized in several advanced applications on the basis of results obtained in the course of this study

Technology Diffusion on the International Trade Network

Technological innovations generate knowledge spillovers-non-innovators benefit through the adoption, imitation, and extension of new technologies. International trade facilitates technology diffusion by providing importing countries access to technical knowledge that they can potentially internalize. Previous studies of the effect of trade on technology diffusion typically only consider the impact of direct (bilateral) trade on indirect measures of technology (e.g., total factor productivity). We contend that the analysis of trade's impact on technology diffusion would be more accurately assessed by using direct measures of specific technologies (e.g., intensity levels) and by allowing for the influence of both the direct and indirect effects of trade in the analysis. The latter is accomplished by modeling the international trade system as a weighted network, which quantifies both direct and indirect trade linkages. Combining trade data with data on the adoption of specific technologies, we find that the network effects of trade play a significant role in technology diffusion. In most cases, countries that are better-connected on the trade network have higher technology intensities. Further support for the importance of trade is provided by the finding that for "outdated" technologies, better-connected countries have lower technology intensities because of their adoption of newer, substitute technologies. © 2016 Wiley Periodicals, Inc

Accelerated microwave curing of fibre-reinforced thermoset polymer composites for structural applications: A review of scientific challenges

Accelerated curing of high performance fibre-reinforced polymer (FRP) composites via microwave heating or radiation, which can significantly reduce cure time and increase energy efficiency, has several major challenges (e.g. uneven depth of radiation penetration, reinforcing fibre shielding, uneven curing, introduction of hot spots etc). This article reviews the current scientific challenges with microwave curing of FRP composites considering the underlying physics of microwave radiation absorption in thermoset-matrix composites. The fundamental principles behind efficient accelerated curing of composites using microwave radiation heating are reviewed and presented, especially focusing on the relation between penetration depth, microwave frequency, dielectric properties and cure degree. Based on this review, major factors influencing microwave curing of thermoset-matrix composites are identified, and recommendations for efficient cure cycle design are provided

Firm performance in networks: the interplay between firm centrality and corporate group size

Corporate groups or networks, which are defined as collections of two or more legally independent firms connected through ownership ties, are prevalent in both developed and developing countries. The separate effects of firm centrality and corporate group size on firm performance have been largely discussed in the literature. However, the effect of their interaction remains underexplored. This paper attempts to fill the gap by introducing a new normalized measure of firm centrality independent of corporate group size. Our empirical analysis is based on a set of global corporate networks encompassing 17.8 million firms and the ownership ties between them extracted from the ORBIS database in 2014. We further investigate the firm performance in the corporate networks above by gathering financial information on 483,835 Italian firms from the AIDA database from 2014 to 2016. We find a positive relationship between firm centrality and firm performance, but the significance of the relationship decreases as corporate group size increases

Pathways into Assisted Living Communities: Admission Limitations and Assessment Requirements Across the United States.

Objectives Limitations to admission play a critical role in shaping the composition of residents residing within licensed assisted living (AL) communities. Design We document variation across 165 licensure classifications in how state agencies limit who AL communities may admit and what assessments are required to make those determinations. Setting and Participants AL regulations and licensed AL communities across all 50 states in 2018. Methods We estimated the proportion of all licensed AL communities regulated by admission limitations and identified groups consisting of those that limit admission based on a health-related condition, specified behavior, mental health condition, and/or cognitive impairment as well as those that impose no limitations to admission. We also estimated the proportion of all licensed AL communities required to conduct assessments at time of admission. Results The largest group of ALs (29% nationally) is governed by regulations limiting the admission of persons with a health condition. The next largest group of AL communities (23.6%) limit admissions based on health, specified behavior, mental health conditions, and cognitive impairment. In contrast, 11.1% of licensed AL communities have no regulations restricting admissions. We also found that more than 8 of every 10 licensed communities were required to have residents complete a health assessment at admission, but less than half were required to complete a cognitive assessment. Conclusions and Implications The variation we observe implies that state agencies have created multiple licensure classifications that serve as a mechanism for sorting types of residents into settings based on their need (eg, health, mental health, cognitive). Although future research should investigate the implications of this regulatory diversity, the categories outlined here may be helpful to clinicians, consumers, and policy makers to better understand the options in their state and how various AL licensure classifications compare to one another