Mechanical properties of hydrophilic copolymers of 2‐hydroxyethyl methacrylate with ethyl acrylate,n‐butyl acrylate, and dodecyl methacrylate

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Abstract
Copolymers were prepared of 2‐hydroxyethyl methacrylate, which is strongly hydrophilic, with hydrophobic comonomers having a low glass transition temperature, i.e., ethyl acrylate, n‐butyl acrylate, and dodecyl methacrylate. The glass transition temperature, Tα (1 Hz), of polymers in the dry state (xerogels) was determined by means of dynamic mechanical measurements. The dependence of Tα on composition in all the three series of copolymers was described in terms of a one‐parameter equation. The equilibrium swelling of copolymers in water decreases more steeply than the weight fraction of 2‐hydroxyethyl methacrylate. When swollen in water to equilibrium, all copolymers with ethyl acrylate or n‐butyl acrylate are in the rubber‐like state; their tensile modulus E assumes values in the range 0.17–0.50 MPa. While poly(2‐hydroxyethyl methacrylate) has the modulus E = 0.39 MPa, the tensile strength σu = 0.32 MPa, and the strain‐at‐break ϵu = 1.81, for the weight fraction of the comonomer in the range 0.36 ⩽ w2 ≤ 0.56 it is possible to achieve σu and ≤ u lying in the respective ranges 0.7–0.9 MPa and 5–7. Copolymers with the dodecyl methacrylate content w2 < 0.2 or w2 > 0.8 are rubberlike, and at 0.30 ≤ w2 ≤ 0.62 they become leathery; the latter have the modulus E and strength σu within the ranges 12–32 and 3–4 MPa, respectively. The stress–strain curves of these copolymers evidence yielding and orientation hardening which have been tentatively explained by the nonhomogeneous composition and structure of the copolymers.

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