Dual Composition Block Copolymers

Abstract

Dual composition block copolymers made from conjugated diene and monovinyl aromatic monomers in batch organolithium initiated polymerization show advantageous performance in the production of crosslinked microcellular rubber compounds and pressure sensitive hot melt adhesives. The block copolymers are partially coupled molecules with a coupling agent linking inner monovinyl aromatic blocks. An un-coupled low molecular weight fraction has greater monovinyl aromatic repeat unit content than a coupled high molecular weight fraction. Crosslinked microcellular rubber articles made from the block copolymers exhibit lower density, smaller and more homogeneous cell size, higher softness and higher resiliency than prior art block copolymers. Rubber compounding of formulations comprising the block copolymers proceed at slightly lower torque and slightly lower temperature than with prior art block copolymers. Pressure sensitive hot melt adhesives formulated with the block copolymers are very well suited for labels, exhibiting higher tack and higher softening temperature than those made from prior art block copolymers.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to U.S. Provisional Patent Application Ser. No. 62 / 782,668 filed on Dec. 20, 2018, which is incorporated by reference.BACKGROUND OF THE INVENTION1. Field of the Invention[0002]This present invention is directed to dual composition block copolymers of conjugated diene and monovinyl aromatic monomers and more particularly to microcellular crosslinked rubber compounds comprising dual composition block copolymers. The novel dual composition block copolymers of the invention can be used to produce microcellular crosslinked rubber compounds with closed cells of homogeneous size, without blistering defects, with improvements in softness and higher resilience.2. Description of the Related Art[0003]Microcellular rubber compounds have widespread application in the manufacture of a variety of products such as shoe soles, sandals, cushioning pads, floating articles, sound dampening sheets, vibration dampening material...

AI Technical Summary

Benefits of technology

[0020]The compositions of the invention enable to accomplish the compounding stage of crosslinked microcellular rubber production in internal batch mixers, such as a Banbury, at reduced temperature, which is beneficial to avoid premature expansion of the chemical blowing agent and to avoid premature crosslinking problems. The compositions of the invention also provide the advantage of negligible shrinking of the microcellular compound during the crosslinking stage. Shaped articles produced with the compositions of the invention exhibit excellent surface appearance, absent of blisters, high softness and high resilience.

[0021]The invention also provides hot-melt pressure sensitive adhesive formulations comprising a novel dual composition block copolymer, among other typical ingredients for this class of adhesives. It has been un-expectedly found that hot-melt pressure sensitive adhesive comprising this novel dual composition block copolymers have improved tack and service temperature range.

Problems solved by technology

In the time elapsed between end of expansion and optimum crosslinking attainment, foam rubber compounds tend to shrink.

Nevertheless, the compositions are disadvantageous, since they include chloro-hydrofluorocarbons as blowing agents, which are harmful to the environment, and exhibit quite large cell size of 0.6 to 1.1 mm.

Therefore, all of them have the disadvantage of requiring high compounding temperatures.

This is because end-blocks rich in vinyl aromatic repeat units of the block copolymers therein disclosed, form an intermolecular physical network that softens adequately as to flow only above 120° C. This high operating compounding temperature may cause premature decomposition of the chemical blowing agent and / or premature crosslinking onset.

This is particularly restrictive when compounding is performed in batch mixers, such as in a Banbury.

Nevertheless, crosslinked microcellular rubber compounds comprising the kind of block copolymers disclosed therein have the disadvantages of non-homogeneous cell size, blister appearance defects, low softness and low resilience.

Nevertheless, they still confer hardness and low resilience to microcellular crosslinked rubber compounds.

Moreover, the continuous anionic polymerization process lacks the flexibility of a batch process to switch polymerization recipes to get different rubber grades without expending off-grade transition production.

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