Amorphous, Elastic AB Copolymer Networks from Acrylates and Poly[(L‐lactide)‐ran‐glycolide]dimethacrylates

Abstract

Shape-memory polymers (SMP) are dual shape materials, which can fix a temporary shape besides their original shape. The process of deformation under application of an external stress above a transition temperature (T trans ) and fixation by cooling below T trans is called programming. The original, permanent shape can be recovered by application of heat. [1][2][3][4][5] Heating could be realized directly by an increase in environmental temperature or indirectly by exposing to alternating magnetic fields [6,7] or illuminating with IR-light. [8] Shapememory polymers have a high innovation potential as biomaterial, especially for minimally invasive surgery. One basic concept in the development of biodegradable polymer systems with shape-memory properties is based on covalently crosslinked polymer networks, [9][10][11][12] containing switching segments from semi-crystalline poly(e-caprolactone) [10,11,13] or poly[(e-caprolactone)-co-glycolide]. [12] The latter ones enable an accelerated hydrolytic degradation because of the presence of easily hydrolizable ester bonds in the form of glycolate ester bonds. [12,14] Another approach is the development of AB copolymer photoset networks, which are obtained from poly(e-caprolactone)dimethacrylate with n-butylacrylate or cyclohexylmethacrylate by UV-crosslinking. [10,11] These polymer networks showed excellent shape-memory properties and as tested so far good tissue-compatibility, in cell culture and in vivo tests. [15][16][17][18][19] Amorphous polymer networks were developed based on poly[(L-lactide)-ran-glycolide)] chain segments. [20,21] This material is transparent and has a shape-memory capability, but its mechanical properties have to be further improved. Polymer networks from poly[(L-lactide)-ran-glycolide)]dimethacrylates (DM) tend to be brittle below the glass transition temperature T g of 55°C and are difficult to handle in the course of the network synthesis and extraction without destroying the samples. The incorporation of a second amorphous phase with a low glass transition temperature (T g,l ) into these materials, which keeps the material elastic, is a potential strategy to effectively improve the elastic properties of poly[(L-lactide)-ran-glycolide]-segment based networks. Formation of an amorphous mixed phase is supposed to allow an adjustment of the switching temperature for the shape-memory effect to a temperature range between roomand body temperature.In a first approach, to obtain dilactide-based amorphous polymer networks with increased toughness and elasticity at room temperature, multi-phase polymer networks were synthesized from amorphous and degradable ABA triblock macrodimethacrylates based on poly(rac-lactide)-b-poly(propylene oxide)-b-poly(rac-lactide). Atactic poly(propylene oxide) (PPG) with a number average molecular weight M n of 4000 g mol -1 and a low T g of -73°C formed the B-block while the molecular weight of A-blocks from poly(rac-lactide) was varied. Variation in this block length resulted in networks with a T g varying between 11°C ...

Shape Memory Polymer Research

“…Along similar lines, Kelch et al (9) prepared conetworks of PLGA-dimethacrylate and two alkyl acrylates, with an aim at achieving an elastomeric yet T g -based SMP akin to the SMPs of Rousseau & Mather (30). (Ordinarily, T g -based SMPs feature glassy tensile moduli in excess of 1 GPa.)…”

“…(Ordinarily, T g -based SMPs feature glassy tensile moduli in excess of 1 GPa.) As such, Kelch et al (9) sought an interpenetrating network structure of PLGA glass and alkyl acrylate elastomer, which was achievable for compositions incorporating the hexyl acrylate monomer. Tensile moduli in the range of 10 to 300 MPa were achieved, and good SM characteristics of fixing and recovery were observed.…”

In Situ X‐Ray Scattering Studies of Poly(ε‐caprolactone) Networks with Grafted Poly(ethylene glycol) Chains to Investigate Structural Changes during Dual‐ and Triple‐Shape Effect

“…While in AB polymer networks both segments contribute to the overall elasticity of the polymer network, [5] the elasticity in grafted polymer networks is mainly determined by the crosslinking segments. [6,7,10] A versatile synthesis route for SMP networks is based on macrodimethacrylates [11][12][13] obtained from (co)polyesterdiols [14] as starting materials. For the present study a poly(e-caprolactone) network with grafted poly(ethylene glycol) side chains (CLEG) that exhibits two distinct melting transitions T m,PEG (T m,A ) and T m,PCL (T m,B ) was investigated.…”

PLGA−POSS End-Linked Networks with Tailored Degradation and Shape Memory Behavior

“…PLGA materials are now not only used as delivery vehicles for drugs and other therapies but also;in manipulated forms;to target cancer, 1 molded into load-bearing geometries such as a screw, 2 to image targeted areas, 3 and can be switched from a temporary shape into a permanent shape through heat or other stimulation. 4,5 This last property, called shape memory, allows for unique possibilities. For thermally triggered shape memory polymers (SMPs), heat is used to raise the sample above some transition temperature so that the sample is rubbery and deformation can take place.…”