EFFECT OF CROSS-LINKING ON THE PROPERTIES OF POLY(2-HYDROXYETHYL METHACRYLATE) HYDROGELS

By means of gamma-irradiation 2-hydroxyethyl methacrylate has been copolymerized in bulk with two different tetrafunctional monomers, ethylene glycol dimethacrylate and 1,3-bis(acryloxymethyl) tetramethyl disiloxane and with a hexafunctional monomer, 1,1,1-trimethylolpropane trimethacrylate. The resultant xerogels were subsequently swollen to equilibrium in water. In order to allow a comparison among the three crosslinkers, their molar masses and functionalities were taken into account, the theoretical crosslink concentrations being varied from 0.032 to 0.644 mol dm-3. The relative hydrophobicity of the three crosslinkers was found to have a significant effect on both the equilibrium swelling and elastic modulus of the swollen gels. Non-freezing water in several gels crosslinked with 1,1,1-trimethylolpropane trimethacrylate was analysed by differential scanning calorimetry (DSC). The proportion of non-freezing water in the gel relative to the overall water content was found to increase with increasing crosslink density

PREPARATION AND CHARACTERIZATION OF SOME LINEAR COPOLYMERS AS PRECURSORS TO THERMOPLASTIC HYDROGELS

The free radical copolymerization of N-vinyl-2-pyrrolidone (VP) with methyl methacrylate (MMA) was carried out to high conversion using 2,2'-azobisbutyronitrile (AIBN) in hexane at 70-degrees-C in the presence of a graft dispersant polymer based on poly(lauryl methacrylate). A stepwise semi-continuous procedure was employed in order to suppress the drift in composition during the conversion. The compositions of the copolymers, determined by i.r. and C-13-NMR, ranged from 23 to 73 wt% VP and the variation of T(g) with composition accorded well with the Fox equation. These linear copolymers were completely soluble in benzyl alcohol, chloroform, 1,2-dichloroethane, dioxane and DMF, but in other liquids they were insoluble, partially soluble or.swollen depending on the composition. Osmometry and light scattering measurements on solutions showed that the copolymers were considerably polydisperse in molar mass but homogeneous in chemical composition. Dry films cast from solution become partially soluble in water when the VP content is > 62 wt%. However, at lower contents of VP, the copolymers swell in water to produce white opaque, elastic hydrogels in which the hydrophobic sequences are considered to behave similarly to chemical crosslinks

QUANTITATIVE-ANALYSIS OF COPOLYMERS BY FTIR

Quantitative analysis of copolymers is described in detail for a series of copolymers of 2-[(phenylamino)carbonyl]oxyethyl methacrylate and 1-methyl-2-phenoxyethyl methacrylate. Particular emphasis is placed on aspects optimising the accuracy of the technique. Thus the irreproducibility resulting from the use of cast films is overcome when using solutions. The criteria of most appropriate solvent are established. Very satisfactory calibration is afforded by blends of the two homopolymers in solution, thus providing an absolute calibration and obviating the use of model compounds or copolymers of known composition

REACTIVITY RATIOS FOR NEW COPOLYMERIZATIONS RELEVANT TO THERMOSETTING RESINS

Free radical copolymerizations of four new systems, namely (1) methyl methacrylate (MMA) with beta-acryloxypropionic acid (AOPA); (2) MMA with p-styrene sulphonyl chloride (SSC); (3) 2-[(phenylamino) carbonyl] oxyethyl methacrylate (PCOMA) with 2-phenoxyethyl methacrylate (PEMA); and (4) PCOMA with 1-methyl-2-phenoxyethyl methacrylate (MPEMA), have been carried out at 60-degrees-C for systems 1 and 2 and at 70-degrees-C for systems 3 and 4. The copolymer compositions were analysed by acid base titration for system 1 and by FTIR for systems 2-4. The monomer reactivity ratios as well as the 95% individual confidence intervals and 95% joint confidence intervals were calculated from the Kelen-Tudos method, the Extended Kelen-Tudos method, and from a new iterative linear method by Mao and Huglin. The results show that all these copolymerizations are strictly linear systems describable by the Mayo Lewis equation based on the terminal model and that accurate reactivity ratio data can be obtained. The Q-e values of the monomers AOPA and SSC have been estimated. Some physical properties of AOPA, PEMA and MPEMA are also presented for the first time